Round duct is employed to attach involving fittings, extras and flex duct. Manufactures usually stock regular lengths, but In case you have your individual spiral equipment you could fabricate any size. On new builds, plasterers can plaster above capping much better than oval conduit, if mounted on to the blockwork. https://paxtonshwkx.ageeksblog.com/35425828/5-simple-statements-about-round-conduit-explained